Self-cleaning intake screens are well known in the art. The earliest of such devices simply employed some mechanism to cause the screen, generally cylindrical in shape, to rotate within the stream or waterway. A water vacuum is generated inside the cylindrical screen, drawing water through the screen for filtration. As the screen rotates, any debris trapped on its upstream side would be washed away as it turns downstream. More sophisticated devices employ some sort of backwash system which, either continually or at periodic intervals, spray a high pressure jet of water or air against the screen in an attempt to blow debris off of and away from the outside of the screen. However, most self-cleaning intake screen designs are complicated and/or do not effectively keep the screen free from debris.
More recently, brushes and scrapers have been added to the outside of cylindrical screens, to scrape off debris and silt from the outer surface of the screen as the screen rotates, so that water flow through the screen to the interior of the screen is not unnecessarily impeded. However, for many applications, the interior of the screen still experiences an intolerable build up of debris and silt. For example, one application involves a screen made of wedge wires, which are thick wire strands that extend circumferentially around a support structure. The support structure includes longitudinally extending support members that are attached to the inside surface of the wedge wire screen, and are spaced one or several inches apart. It has been found that an external brush sweeping across the outer surface of the wedge wire screen fails to adequately clean the inside surface of the wedge wire and the support members, as well as possibly the laterally facing surfaces of the wedge wires. Spacing the support members further apart can reduce silt buildup, but then the screen no longer has the desired structural integrity, and the cylinder can lose its roundness as the wedge wire tends to lie flat between the support members.
It is also known to place a spirally oriented, motorized cleaning brush on the inside surface of a rotating cylindrically shaped screen, where the brush rotates in the opposite direction as the moving direction of the screen. However, such motorized cleaning brushes will not work with wedge wire type screens such as the one described above, because the brush will continually encounter the support members, which are not flush with the inside surface of the wedge wire screen. Thus, any brushes designed to clear the support members will not adequately clean the interior and lateral surfaces of the wedge wire. Moreover, it is expensive and difficult to include a separate motor, inside the cylindrical screen, to operate the rotating brush.
There is a need for an intake screen that reliably and effectively cleans itself, even its interior surfaces, without adding the complexity of additional motors.